The present disclosure relates to semiconductor structures and, more particularly, to devices with slotted active regions and methods of manufacture. The method includes: forming a mandrel on top of a diffusion region comprising a diffusion material; forming a first material over the mandrel and the diffusion region; removing the mandrel to form multiple spacers each having a thickness; depositing a second material over the spacers and the diffusion material; and forming slots in the diffusion region by removing a portion of the second material over the diffusion region and the underlying diffusion material.